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Re: The Engineering Paradigm (WAS Re: Op

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>Actually, the Challenger disaster was the result of considering ECONOMICS 
>and 
>PUBLIC RELATIONS ahead of SAFETY. 
That was only one of the causes. Like the Titanic sinking there were 
several 'but-fors.' The design itself was tricky. I'd worked with an 8 
foot diameter test tank which had a clevis type joint and O-ring, and it 
was always a flaming bitch to assemble. When I saw a diagram of the joint 
a day or two after the disaster, I was about 99% certain that it was a 
seal problem like we'd had with the Perry test tank.

One or the other of the Feynman books ('What Do you Care What Other 
People Think?' or 'Surely You're Joking Mr Feynman,') has a couple of 
chapters on the Challenger explosion. They'd had problems during design 
and test and in previous launches, but didn't do much about the design. 
Joint assembly was also tricky which led to difficulty with mating the 
seal and the sealing surfaces. Feynman was widely credited with 
discovering the seal problem with his video demonstration, but he seems 
to say that he was put onto the idea from an Air Force officer on the 
committee. Feynman has a detailed discussion of all the statistical arm 
waving that NASA used to convince itself of reliability, in which they 
progressively lowered the bar on thermal requirements. The last straw was 
apparently pressure from the supreme NASA PhB to get Christa McAuliffe 
into space because she was scheduled to talk to Reagan that day. Between 
the design, the failure to deal with problems uncovered testing, foolish 
interpretation of cooked-up reliability statistics and management and 
political pressure, you can pick any or all as causes. 

In philosophical terms, that's and interesting thing about disasters of 
all sorts--from the Johnstown flood to the TMI accident sinking to Pearl 
Harbor. All were chains of events, the absence any one of which could 
have made it into a non-event.

>The Bronx Whitestone Bridge (I believe) was designed to the same slenderness 
>as the Tacoma Narrows Bridge.  I remember crossing the bridge in the 1940's 
>when it was being reinforced and my father explaining that they were putting 
>stiffening trusses on it.
Petroski mentions this alteration and some others made after the Tacoma 
Narrows bridge came down. When I was a kid in Cincinnati in the 40's 
bridges were fascinating, especially Roebling's suspension bridge across 
the Ohio, because of the film of the Tacoma Narrows Bridge. They still 
fascinate me. What's really interesting about TN is the curious response 
of the towers and cable--with all that weird dynamic loading  both look 
absolutely rock solid even as the deck drops into the water. No apparent 
damage to either the towers or cable--I find that curious.

Christopher Wright P.E.    |"They couldn't hit an elephant from
chrisw(--nospam--at)skypoint.com        | this distance"   (last words of Gen.
___________________________| John Sedgwick, Spotsylvania 1864)
http://www.skypoint.com/~chrisw


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